Recognizing the importance of needle sharing as a causal factor in acquiring viral infections and later developing cancer led to a collaborative project with Drs. Steffanie Strathdee at the University of California-San Diego, Karl Broman at the Johns Hopkins University - Bloomberg School of Public Health, and Dr. David Vlahov at the New York Academy of Medicine who evaluate the Baltimore Needle Exchange Program (NEP). Needle sharing is a common means by which intravenous drug users (IVDUs) acquire viral infections, most commonly hepatitis B (HBV), hepatitis C (HCV) and HIV-1. The hepatitis viruses are causative agents in liver cirrhosis and hepatocellular carcinoma, and HIV-1, as the causative agent of AIDS, has cancer outcomes of lymphomas, Kaposi's sarcoma and other rare cancers.[unreadable] [unreadable] Work this year has focused on developing a highly sensitive assay methodology and a theoretical context for determination of mixtures with pentanucleotide single tandem repeats (STRs). Current assays are able to detect four loci with 0.1 ng or less of DNA. Determination of sensitivity and specificity with blinded samples and the new methodologies was recently accepted along with a theory and methodology paper that was published.[unreadable] [unreadable] These methods were developed to test several hypotheses related to needle sharing and viral infection. One, self-reports of multi-person use of syringes underestimate true levels. Two, multi-person use of syringes has significantly declined over time since the NEP was introduced. Three, NEP syringes acquired by secondary exchange will have circulated longer and will have higher rates of multi-person syringe use, compared to NEP syringes acquired by primary exchange. Four, syringe sharing can identify high-risk seronegatives for our HIV-1 genetic epidemiology studies aimed at identifying infection resistance genes. Preliminary analysis of syringe exudates has identified a high level of sharing and that work is currently being written up for publication.